What if my existing system operates fine (to me), even with poor duct work?

Site Maintenance

HVAC-Talk site will be slow for the next few days. It's normal site/server maintenance. Thx -Dad

Welcome to HVAC-Talk.com, a non-DIY site and the ultimate Source for HVAC Information & Knowledge Sharing for the industry professional! Here you can join over 150,000 HVAC Professionals & enthusiasts from around the world discussing all things related to HVAC/R. You are currently viewing as a NON-REGISTERED guest which gives you limited access to view discussions

To gain full access to our forums you must register; for a free account. As a registered Guest you will be able to:

Participate in over 40 different forums and search/browse from nearly 3 million posts.

What if my existing system operates fine (to me), even with poor duct work?

I have a (1995) 1700 sq ft Cape in north Maryland running a 1995 Rheem 3 ton (10 SEER?) and WeatherKing forced hot air oil burner (140k input!). I am the first owner, have not had one problem with this system - not one. To me, the cooling is decent - humidity feels ok when set around 76F. No issues on the hottest of days. This past month's electric (July) was $200 (but I have a turn back thermostat running from 6am-4pm). The oil burner has a .85 nozzle to increase cycle time. By far, heating costs far outweight cooling costs, but the heating season is longer. My small house has 8 of Andersen's largest residential skylights, and most (Andersen) windows run down to within a foot of the floor (lots of glass). That's probably not enough to warrant the likes of a 140k oil burner, but is an indication that this house has LOTS of glass.
So, if I am relatively happy with the existing system, even with the undersized return (and whatever else in the duct work is poorly designed which I do not know about), should I really be concerned with duct work mods at time of new install? Will the expense easily be paid back in 10 years or too hard to answer with this limited info? The plenum and main are made from that crappy duct board - that could be mod'ed easily. But the house is a Cape, and getting to any vertical runs would be prohibitive (most interior walls consist of 3/4" pine tonque and groove over drywall).

I've even used one of those Lasko drum humidifiers in the winter. Never any issue (that I know of) with the ductboard. No smells, I'm never sick. I thought for sure that humidifying that ductboard would create some nasty mold; if it is, I can not tell. So overall, I feel I've gotten away with many 'improper' system design issues, yet I am reasonably pleased with the performance.

I have a (1995) 1700 sq ft Cape in north Maryland running a 1995 Rheem 3 ton (10 SEER?) and WeatherKing forced hot air oil burner (140k input!). I am the first owner, have not had one problem with this system - not one. To me, the cooling is decent - humidity feels ok when set around 76F. No issues on the hottest of days. This past month's electric (July) was $200 (but I have a turn back thermostat running from 6am-4pm). The oil burner has a .85 nozzle to increase cycle time. By far, heating costs far outweight cooling costs, but the heating season is longer. My small house has 8 of Andersen's largest residential skylights, and most (Andersen) windows run down to within a foot of the floor (lots of glass). That's probably not enough to warrant the likes of a 140k oil burner, but is an indication that this house has LOTS of glass.
So, if I am relatively happy with the existing system, even with the undersized return (and whatever else in the duct work is poorly designed which I do not know about), should I really be concerned with duct work mods at time of new install? Will the expense easily be paid back in 10 years or too hard to answer with this limited info? The plenum and main are made from that crappy duct board - that could be mod'ed easily. But the house is a Cape, and getting to any vertical runs would be prohibitive (most interior walls consist of 3/4" pine tongue and groove over drywall).

I've even used one of those Lasko drum humidifiers in the winter. Never any issue (that I know of) with the ductboard. No smells, I'm never sick. I thought for sure that humidifying that ductboard would create some nasty mold; if it is, I can not tell. So overall, I feel I've gotten away with many 'improper' system design issues, yet I am reasonably pleased with the performance.

The 2.5 summer design for Baltimore MD is 89F dry bulb; 76F wet bulb or around a high 55.5% RH; humidity is a big comfort factor.
Those 10-SEER condensers were good for dehumidification.

Concerning a new system for your location & weather; I'd want a 13 or 14-SEER system & sized for optimal dehumidification; for optimal dehumidification make sure it has a TXV metering device on the indoor coil & you'll probably want the blower running at 350-CFM per ton of cooling.

You'll also want a digital temperature differential adjustable 1 to 9 SWING RM/TH; or an adjustable cycles per hour RM/TH.

Under-sizing the A/C a little is also helpful to get decently long runtimes during the moderate temp high humidity times in MD. Discuss it with the HVAC contractor...

Get that return air plus the filter area sized for optimal efficient performance; the newer units need correct design to achieve near their SEER Ratings.

Compared to my electric bill your's seems high; don't expect much savings with a new system unless the install & entire setup is done properly to high specification standards.

Generally, a six-inch clearance between the air conditioning evaporator coil and the heat exchanger will provide adequate airflow through the evaporator coil. (Mfg'ers instructions)

If it's horizontal or an upflow oil heating system, I hope there is at least 6" between the top of the furnace & the evaporator coil; that's to prevent an airflow restriction causing too much back-pressure. this is very important; see that it is done properly on any new install.

Would you be happier spending less money each month and lowering the impact on the energy resources that effect everyone in the world?

honestly, I'm not much into the green scene. Unless I can EASILY recoop (in less than 10 years) the extra expenditure to make a 14 SEER operate at peak efficiency, and put a 20%+ dent in my existing oil bill (over and beyond what a poorly matched new furnce provides), I'll take an inefficient realiable system as similar to what I have been living with, whatever make/model is most similar to a '95 vintage that I own. A contractor may state these gains for an optimzed system, but in the end, how do you really know? A non-optimzed system, using modern equipment, may provide those type of savings even if not constructed well as a whole system. Being spoiled by 17 years of HVAC issue-less living, reliability trumps all, for me. Not one peep from my A/C or oil burner - never, ever, ever a problem. I'll take the peace of mind and realiabiltiy, even at the expense of less effieciency and higher utils. I only buy Jap cars as well, fwiw - NOTHING beats having a reliable car/system/whatever. I'll pay for that reliability even if the gas mileage is poor. YMMV.

You can keep your oil burner and replace the ac unit with a heat pump ,that will on oil usage

lol. thanks for the idea, but I do like WARM air from a forced hot air unit. Know lots of people around here with heat pumps - don't know their setup details, but overwhelming majority state that on 'cold' days their houses feel 'cold', as long as they do not kick-in the backup (electric) heat.
Could I use a heat pump with a small(er) oil burner, the oil burner acting as the backup heat source? Or would this be an expensive proposition? thx.

Going to oil hybrid you should recover the incremental cost in 2-5 years. Expect a more evenly comfortable home also because it'll now have multi-stage heat......

Could you please dumb this down for me a bit? By 'oil hybrid', do you mean exactly what I currently have? Cooling by A/C, heating by oil? What is the 'incremental cost'? And what constitues multi-stage heat? Is this found even on the most basic gas/oil burners today? Do you have to have a 2 stage A/C, or is it something totally independent of a/c? Is it just a variable speed blower, or something else? thx.

It means that you would have a heat pump instead of just an A/c unit. The heat pump would heat the house on milder temp days. The oil furnace on the colder days that the heat pump can't maintain temp in the house.

The cost difference to install dual-fuel should not discourage you from going that route. I have yet to have a customer regret going dual-fuel (and these are those that for some reason did not get rid of the oil or gas and go heat pump) and make much about the money they save.

Also consider that the system you currently have has a t-stat that you control. You want it 72, you set it there, right? With the heat pump, you will also have a t-stat you will control, and if 72 is the desired temp, you set it there. Converting to heat pump, you will still have the ability to heat your house to the desired temp, though it is said that for that "hot heat" you may run a little higher on the setpoint.

But I am confident that 1) I do not think you will regret the cost spent to go dual-fuel; 2) you will be pleased with the performance of the heat pump.

Worst-case scenario would be you are not satisfied, and you do not use it. But if you neglect to get the dual-fuel to save a little money...you will never know. That should already be bugging you...lol.